Upstream frequency response measurement and characterization

ABSTRACT

Upstream frequency response measurement and characterization. Signaling is provided between respective communication devices within a communication system. Based upon at least one of these signals, one of the communication devices captures a number of sample sets corresponding thereto at different respective frequencies (e.g., a different respective center frequencies, frequency bands, etc.). Then, spectral analysis is performed with respect to each of the sample sets to generate a respective and corresponding channel response estimate there from. After this number of channel response estimates is determined, they are combined or splice together to generate a full channel response estimate. In implementations including an equalizer, different respective sample sets may correspond to those that have undergone equalization processing and those that have not.

CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS ProvisionalPriority Claims

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. §119(e) to the following U.S. Provisional Patent Applicationwhich is hereby incorporated herein by reference in its entirety andmade part of the present U.S. Utility Patent Application for allpurposes:

1. U.S. Provisional Patent Application Ser. No. 61/467,659, entitled“Upstream frequency response measurement and characterization,” filedMar. 25, 2011, pending.

BACKGROUND OF THE INVENTION

1. Technical Field of the Invention

The invention relates generally to communication systems; and, moreparticularly, it relates to frequency response measurement and/orcharacterization of communication channels within such communicationsystems.

2. Description of Related Art

Data communication systems have been under continual development formany years. With such a communication system, characterization and/orestimation of any of a number of different parameters may be performed.For example, the communication channels are communication links overwhich signals traverse between communication devices may be analyzed forany of a number of reasons. For example, certain communication devicesmay perform appropriate processing of signals transmitted there from orreceived thereby based upon such characterization to improve the overalloperation not only of those respective communication devices but theoverall communication system. While the need to perform suchcharacterization and/or estimation of various parameters withincommunication systems is well known, the prior art nonetheless continuesto provide less than ideal solutions by which this may be made. As such,there continues to be a need to make such characterization and/orestimation of various parameters within communication systems in abetter, more accurate, and more efficient way.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1, FIG. 2, and FIG. 3 illustrate various embodiments ofcommunication systems.

FIG. 4 illustrates an embodiment of communications between respectivecommunication devices in a communication system, and respective channelresponse estimates made with respect to different respective centerfrequencies and/or frequency bands.

FIG. 5, FIG. 6, FIG. 7, and FIG. 8 illustrates various respectiveembodiments of respective channel response estimates at differentrespective center frequencies and/or frequency bands, and theirrelationship to a full channel response estimate.

FIG. 9 illustrates an embodiment of a communication device.

FIG. 10 illustrates an embodiment of a multiple devices, components,functional blocks, etc. employed for different respective centerfrequencies and/or frequency bands.

FIG. 11 illustrates an embodiment of a method for operating at least onecommunication device.

FIG. 12 illustrates an alternative embodiment of a method for operatingat least one communication device.

DETAILED DESCRIPTION OF THE INVENTION

Within communication systems, signals are transmitted between variouscommunication devices therein. The goal of digital communicationssystems is to transmit digital data from one location, or subsystem, toanother either error free or with an acceptably low error rate. As shownin FIG. 1, data may be transmitted over a variety of communicationschannels in a wide variety of communication systems: magnetic media,wired, wireless, fiber, copper, and other types of media as well.

FIG. 1 and FIG. 2 are diagrams illustrate various embodiments ofcommunication systems, 100 and 200, respectively.

Referring to FIG. 1, this embodiment of a communication system 100 is acommunication channel 199 that communicatively couples a communicationdevice 110 (including a transmitter 112 having an encoder 114 andincluding a receiver 116 having a decoder 118) situated at one end ofthe communication channel 199 to another communication device 120(including a transmitter 126 having an encoder 128 and including areceiver 122 having a decoder 124) at the other end of the communicationchannel 199. In some embodiments, either of the communication devices110 and 120 may only include a transmitter or a receiver. There areseveral different types of media by which the communication channel 199may be implemented (e.g., a satellite communication channel 130 usingsatellite dishes 132 and 134, a wireless communication channel 140 usingtowers 142 and 144 and/or local antennae 152 and 154, a wiredcommunication channel 150, and/or a fiber-optic communication channel160 using electrical to optical (E/O) interface 162 and optical toelectrical (O/E) interface 164)). In addition, more than one type ofmedia may be implemented and interfaced together thereby forming thecommunication channel 199.

To reduce transmission errors that may undesirably be incurred within acommunication system, error correction and channel coding schemes areoften employed. Generally, these error correction and channel codingschemes involve the use of an encoder at the transmitter end of thecommunication channel 199 and a decoder at the receiver end of thecommunication channel 199.

Any of various types of ECC codes described can be employed within anysuch desired communication system (e.g., including those variationsdescribed with respect to FIG. 1), any information storage device (e.g.,hard disk drives (HDDs), network information storage devices and/orservers, etc.) or any application in which information encoding and/ordecoding is desired.

Generally speaking, when considering a communication system in whichvideo data is communicated from one location, or subsystem, to another,video data encoding may generally be viewed as being performed at atransmitting end of the communication channel 199, and video datadecoding may generally be viewed as being performed at a receiving endof the communication channel 199.

Also, while the embodiment of this diagram shows bi-directionalcommunication being capable between the communication devices 110 and120, it is of course noted that, in some embodiments, the communicationdevice 110 may include only video data encoding capability, and thecommunication device 120 may include only video data decodingcapability, or vice versa (e.g., in a uni-directional communicationembodiment such as in accordance with a video broadcast embodiment).

It is noted that such communication devices 110 and/or 120 may bestationary or mobile without departing from the scope and spirit of theinvention. For example, either one or both of the communication devices110 and 120 may be implemented in a fixed location or may be a mobilecommunication device with capability to associate with and/orcommunicate with more than one network access point (e.g., differentrespective access points (APs) in the context of a mobile communicationsystem including one or more wireless local area networks (WLANs),different respective satellites in the context of a mobile communicationsystem including one or more satellite, or generally, differentrespective network access points in the context of a mobilecommunication system including one or more network access points bywhich communications may be effectuated with communication devices 110and/or 120.

Referring to the communication system 200 of FIG. 2, at a transmittingend of a communication channel 299, information bits 201 (e.g.,corresponding particularly to video data in one embodiment) are providedto a transmitter 297 that is operable to perform encoding of theseinformation bits 201 using an encoder and symbol mapper 220 (which maybe viewed as being distinct functional blocks 222 and 224, respectively)thereby generating a sequence of discrete-valued modulation symbols 203that is provided to a transmit driver 230 that uses a DAC (Digital toAnalog Converter) 232 to generate a continuous-time transmit signal 204and a transmit filter 234 to generate a filtered, continuous-timetransmit signal 205 that substantially comports with the communicationchannel 299. At a receiving end of the communication channel 299,continuous-time receive signal 206 is provided to an AFE (Analog FrontEnd) 260 that includes a receive filter 262 (that generates a filtered,continuous-time receive signal 207) and an ADC (Analog to DigitalConverter) 264 (that generates discrete-time receive signals 208). Ametric generator 270 calculates metrics 209 (e.g., on either a symboland/or bit basis) that are employed by a decoder 280 to make bestestimates of the discrete-valued modulation symbols and information bitsencoded therein 210.

Within each of the transmitter 297 and the receiver 298, any desiredintegration of various components, blocks, functional blocks,circuitries, etc. Therein may be implemented. For example, this diagramshows a processing module 280 a as including the encoder and symbolmapper 220 and all associated, corresponding components therein, and aprocessing module 280 is shown as including the metric generator 270 andthe decoder 280 and all associated, corresponding components therein.Such processing modules 280 a and 280 b may be respective integratedcircuits. Of course, other boundaries and groupings may alternatively beperformed without departing from the scope and spirit of the invention.For example, all components within the transmitter 297 may be includedwithin a first processing module or integrated circuit, and allcomponents within the receiver 298 may be included within a secondprocessing module or integrated circuit. Alternatively, any othercombination of components within each of the transmitter 297 and thereceiver 298 may be made in other embodiments.

As with the previous embodiment, such a communication system 200 may beemployed for the communication of video data is communicated from onelocation, or subsystem, to another (e.g., from transmitter 297 to thereceiver 298 via the communication channel 299).

Referring to the communication system 300 of FIG. 3, this communicationsystem 300 may be viewed particularly as being a cable system. Such acable system may generally be referred to as a cable plant and may beimplemented, at least in part, as a hybrid fiber-coaxial (HFC) network(e.g., including various wired and/or optical fiber communicationsegments, light sources, light or photo detection complements, etc.).For example, the communication system 300 includes a number of cablemodems (shown as CM 1, CM 2, and up to CM n). A cable modem networksegment 399 couples the cable modems to a cable modem termination system(CMTS) (shown as 340 or 340 a and as described below).

A CMTS 340 or 340 a is a component that exchanges digital signals withcable modems on the cable modem network segment 399. Each of the cablemodems coupled to the cable modem network segment 399, and a number ofelements may be included within the cable modem network segment 399. Forexample, routers, splitters, couplers, relays, and amplifiers may becontained within the cable modem network segment 399.

The cable modem network segment 399 allows communicative couplingbetween a cable modem (e.g., a user) and the cable headend transmitter330 and/or CMTS 340 or 340 a. Again, in some embodiments, a CMTS 340 ais in fact contained within a cable headend transmitter 330. In otherembodiments, the CMTS is located externally with respect to the cableheadend transmitter 330 (e.g., as shown by CMTS 340). For example, theCMTS 340 may be located externally to the cable headend transmitter 330.In alternative embodiments, a CMTS 340 a may be located within the cableheadend transmitter 330. The CMTS 340 or 340 a may be located at a localoffice of a cable television company or at another location within acable system. In the following description, a CMTS 340 is used forillustration; yet, the same functionality and capability as describedfor the CMTS 340 may equally apply to embodiments that alternativelyemploy the CMTS 340 a. The cable headend transmitter 330 is able toprovide a number of services including those of audio, video, localaccess channels, as well as any other service of cable systems. Each ofthese services may be provided to the one or more cable modems (e.g., CM1, CM 2, etc.). In addition, it is noted that the cable headendtransmitter 330 may provide any of these various cable services viacable network segment 398 to a set top box (STB) 320, which itself maybe coupled to a television 310 (or other video or audio output device).While the STB 320 receives information/services from the cable headendtransmitter 330, the STB 320 functionality may also supportbi-directional communication, in that, the STB 320 may independently (orin response to a user's request) communicate back to the cable headendtransmitter 330 and/or further upstream.

In addition, through the CMTS 340, the cable modems are able to transmitand receive data from the Internet and/or any other network (e.g., awide area network (WAN), internal network, etc.) to which the CMTS 340is communicatively coupled. The operation of a CMTS, at thecable-provider's headend, may be viewed as providing analogous functionsprovided by a digital subscriber line access multiplexor (DSLAM) withina digital subscriber line (DSL) system. The CMTS 340 takes the trafficcoming in from a group of customers on a single channel and routes it toan Internet Service Provider (ISP) for connection to the Internet, asshown via the Internet access. At the headend, the cable providers willhave, or lease space for a third-party ISP to have, servers foraccounting and logging, dynamic host configuration protocol (DHCP) forassigning and administering the Internet protocol (IP) addresses of allthe cable system's users (e.g., CM 1, CM2, etc.), and typically controlservers for a protocol called Data Over Cable Service InterfaceSpecification (DOCSIS), the major standard used by U.S. cable systems inproviding Internet access to users. The servers may also be controlledfor a protocol called European Data Over Cable Service InterfaceSpecification (EuroDOCSIS), the major standard used by European cablesystems in providing Internet access to users, without departing fromthe scope and spirit of the invention.

The downstream information flows to all of the connected cable modems(e.g., CM 1, CM2, etc.). The individual network connection, within thecable modem network segment 399, decides whether a particular block ofdata is intended for it or not. On the upstream side, information issent from the cable modems to the CMTS 340; on this upstreamtransmission, the users within the group of cable modems to whom thedata is not intended do not see that data at all. As an example of thecapabilities provided by a CMTS, a CMTS will enable as many as 1,000users to connect to the Internet through a single 6 Mega-Hertz channel.Since a single channel is capable of 30-40 Mega-bits per second of totalthroughput (e.g., currently in the DOCSIS standard, but with higherrates envisioned such as those sought after in accordance with thedeveloping DVB-C2 (Digital Video Broadcasting—Second Generation Cable)standard, DVB-T2 (Digital Video Broadcasting—Second GenerationTerrestrial) standard, etc.), this means that users may see far betterperformance than is available with standard dial-up modems.

Moreover, it is noted that the cable network segment 398 and the cablemodem network segment 399 may actually be the very same network segmentin certain embodiments. In other words, the cable network segment 398and the cable modem network segment 399 need not be two separate networksegments, but they may simply be one single network segment thatprovides connectivity to both STBs and/or cable modems. In addition, theCMTS 340 or 340 a may also be coupled to the cable network segment 398,as the STB 320 may itself include cable modem functionality therein.

It is also noted that any one of the cable modems 1, 2, . . . m n, thecable headend transmitter 330, the CMTS 340 or 340 a, the television310, the STB 320, and/or any device existent within the cable networksegments 398 or 399, may include a memory optimization module asdescribed herein to assist in the configuration of various modules andoperation in accordance with any one of a plurality of protocolstherein.

Various communication devices can operate by employing an equalizertherein (e.g., an adaptive equalizer). Some examples of suchcommunication devices include those described herein, including cablemodems (CMs). However, it is noted that various aspects and principlespresented herein may be generally applied to any type of communicationdevice located within any of a variety of types of communicationsystems. For example, while some illustrative and exemplary embodimentsherein employ the use of a CM in particular, though it is noted thatsuch aspects and principles presented herein may be generally applied toany type of communication device located within any of a variety oftypes of communication systems.

Various communication devices (e.g., a cable modem (CM), a cable modemtermination system (CMTS), etc.) may report information there betweenand coordinate operation thereof.

It is again noted that while the particular illustrative example of acable modem (CM) is employed in a number of different embodiments,diagrams, etc. herein, such architectures, functionality, and/oroperations may generally be included and/or performed within any of anumber of various types of communication devices including thoseoperative in accordance with the various communication system types,including those having more than one communication medium type therein,such as described with reference to FIG. 1.

FIG. 4 illustrates an embodiment 400 of communications betweenrespective communication devices in a communication system, andrespective channel response estimates made with respect to differentrespective center frequencies and/or frequency bands. Generallyspeaking, this diagram shows communication between two respectivecommunication devices within the communication system.

After a first communication device receives a signal (e.g., a rangingburst) from another communication device (e.g., a second communicationdevice), the first communication device may be implemented to performcapture of a number of sample sets corresponding to the ranging burst.Each of these respective ranging bursts may correspond to a respectivefrequency and/or frequency band. Spectral analysis of each of theserespective sample sets may be performed to generate a number of upstreamchannel response estimates such that each respective upstream channelresponse estimate thereof corresponds to one of the sample sets. Theserespective upstream channel response estimates may be spliced orcombined together to generate a full upstream channel response estimate.

FIG. 5, FIG. 6, FIG. 7, and FIG. 8 illustrates various respectiveembodiments of respective channel response estimates at differentrespective center frequencies and/or frequency bands, and theirrelationship to a full channel response estimate.

Various of these respective diagrams show alternative in variousembodiments by which respective channel response estimates may be madewith respect to different respective frequencies or frequency bands.

Referring to the embodiment 500 of FIG. 5, as may be seen with respectto this diagram, a number of respective frequency bands are implementedwith respect to a first frequency, f1. Each of the respective centerfrequencies of the higher frequency bands is shown as being a respectiveinteger multiple of the first frequency. In accordance with thisparticular diagram, different respective channel response estimates aregenerated for each of the respective bands, and those channel responseestimates are spliced or combined together to generate a full channelresponse estimate. As may be understood, such a full channel responseestimate is a wideband channel response estimate. In addition, withrespect to this diagram, each of the respective frequency bands extendsdirectly up to a band edge, with no overlap into adjacent bands and withno guard interval in between the respective bands.

Referring to the embodiment 600 of FIG. 6, with respect to this diagram,a number of respective guard intervals (GIs) are implemented at theedges of the respective frequency bands. Such GIs may be viewed asoccurring at the outer limits (e.g., lower and upper) of each respectivefrequency bands in an effort to ensure little or no interaction betweenthe respective frequency bands. In accordance with the respectivechannel response estimates generated by such frequency bands separatedby respective guard intervals, it may be understood that certainsmoothing effects may be made and performed when splicing and combiningtogether the different respective channel response estimates.

Referring to the embodiment 700 of FIG. 7, in this diagram, the variousrespective frequency bands have some overlap with one another. Therespective channel response estimates associated with these respectivefrequency bands may provide a smoother transition and a more seamlesscombination of the respective channel response estimates in generatingthe full channel response estimate.

Referring to the embodiment 800 of FIG. 8, as may be seen with respectto this diagram, the frequency bands are of non-uniform width.Generally, any desired widths of respective frequency bands may beemployed in accordance with generating different respective channelresponse estimates across a relatively wider portion of the frequencyspectrum. For example, there may be some instances in which narrowbandchannels and relatively wider band channels are employed in combinationwith one another in a communication system.

Moreover, there may be some instances in which the center frequenciesand/or frequency bandwidths of the various frequency bands may bemodified over time, such as in accordance with a dynamic or adaptiveimplementation. Any desired partitioning of the frequency spectrum intodifferent respective frequency bands having different respective centerfrequencies may be used in accordance with various aspects, and theirequivalents, of the invention.

FIG. 9 illustrates an embodiment 900 of a communication device. As shownwithin this diagram, a communication device receives a signal, such asfrom a communication link within a communication system or network, andthe signal undergoes appropriate processing by and analog front end(AFE). Such an AFE may be of amended perform any of a number ofoperations including digital sampling, such as by an analog to digitalconverter (ADC), filtering (e.g., in the analog domain and/or thedigital domain), frequency conversion (e.g., such as conversion from acarrier frequency down the baseband), scaling, gain adjustment, etc.Generally, such an AFE may be viewed as performing receipt anddemodulation of a signal received from any communication link. Any of anumber of perspective circuitries, modules, functional blocks, etc. maybe implemented within various embodiments of an AFE.

It is also noted that such a communication device may receiveinformation from one or more other communication devices (e.g., one ormore transmitters) providing some indication regarding operation of oneor more other communication devices within the communication system.

After the AFE, one or more processors (one processor shown within thisembodiment) operate to perform spectral processing of the receivedsignal that has undergone front and a processing by the AFE. Forexample, such a processor is implemented to perform spectral processingto generate different respective upstream channel response estimatescorresponding to different respective sample sets that themselvescorrespond respectively to different respective center frequenciesand/or frequency bands. These different respective upstream channelresponse estimates are then spliced or combined together to generate afull up stringent response estimate covering a relatively broaderfrequency range that each of the individual and respective centerfrequencies and/or frequency bands individually cover.

Any of a number of different types of signal processing may be performedincluding fast Fourier transform (FFT) processing, discrete Fouriertransform (DFT) processing, etc. and/or any other form of signalprocessing including digital signal processing. For example, inalternative embodiments, various types of filtering, such as bandpassfiltering, high pass filtering, etc. including those which may operatein accordance with having adaptive bandwidths (e.g., those being tunabletwo different bandwidths, different respective frequencies, etc.) mayalso be employed. In addition, such a processor may be implemented toperform filtering, and such filtering may be made in combination withanalog filtering (e.g., such as may be performed within the AFE).

FIG. 10 illustrates an embodiment 1000 of a multiple devices,components, functional blocks, etc. employed for different respectivecenter frequencies and/or frequency bands. As may be seen with respectto this diagram, a frequency selector or partition or is operative toprovide different respective frequency bands to different respectivedevices (shown pictorially as processors in this diagram). For example,information and/or signal content associated with a first frequency,frequency band, or channel is provided to a first processor.Analogously, information and/or signal content associated with thesecond frenzy, frequency band, or channels provided to a secondprocessor, and so on. Each of these separately implemented processors isimplemented to generate a channel response estimate corresponding tothat information and/or signal content portion received thereby. Asubsequent processor operates to combine or splice each of theserespective channel response estimates together to generate a fullchannel response estimate.

As may be understood, any of a number of different architectures andimplementations may be made by which different portions of the frequencyspectrum may undergo appropriate processing to generate respectivechannel response estimates corresponding to those different portions ofthe frequency spectrum such that they subsequently undergo splicing orcombination to generate a full channel response estimate for arelatively broader frequency range than any of the individual,respective channel response estimates.

A novel approach is presented herein to measure the amplitude and groupdelay variation of the upstream cable plant within various frequencyranges e.g., 5-42 MHz, 5-65 MHz, 5-85 MHz, or wider. This can be doneusing equalizer taps, FFTs, or raw samples before the FFT.

Use of Equalizer Taps to Estimate Upstream Plant Response.

This is performed as follows. Simultaneously step a spare burst receiverand transmitter (such as cable modem or specialized probe such as adownstream monitor (DMON)) across the upstream band, using frequencysteps of ¼, ½, or ¾ (or some other desired frequency step) the symbolrate, for example. CMAP scheduler should schedule quiet times in theappropriate channels as the probe signal (sent by probe and received byburst receiver) steps across the upstream band.

At each frequency, capture pre-equalizer (e.g., from a transmitterdevice or a first communication device [e.g., a transceiver] such as acable modem) and post-equalizer taps (e.g., from a receiver device or asecond communication device [e.g., a transceiver] such as a cable modemtermination system (CMTS)), gain and timing offset after a long rangingburst. The existing DOCSIS ranging bursts contain a long trainingsequence with known QPSK data which is designed to be a good probe ofthe upstream channel, and which has a known, approximately flatfrequency spectrum.

Splice information from all frequency steps together to produce fullupstream response. Overlap may be used to allow seamless blending of theresponses measured at different frequencies.

The information measured at each frequency step includes pre-equalizertaps from CM, post-equalizer taps converged in burst receiver, timingoffset estimate from nominal as estimated by burst receiver, frequencyoffset estimate from nominal as estimated by burst receiver, and gainoffset estimate from nominal as estimated by burst receiver.

The equalizer taps may be further processed to estimate the upstreamchannel response. In many cases, the channel response may be closelyapproximated by the inverse of the total equalizer response, where thetotal equalizer response includes the pre-equalizer taps, post-equalizertaps, and auxiliary information such as estimated timing offset.

There may be holes (inaccessible bands) in the resulting spectrumestimate where other services such as set-top boxes are transmitting.The missing pieces can be filed with zeros (or other predetermined orconvenient data) to process them in accordance with assembling thespliced spectrum.

Use of direct spectrum calculation (such as FFT) to estimate upstreamplant response

This is performed as follows. Simultaneously step a spare burst receiveror other device capable of performing spectral analysis, and transmitter(such as cable modem or specialized probe such as DMON), across theupstream band, using frequency steps of ¼, ½, or ¾ the symbol rate, forexample. At each frequency, the probe signal is transmitted up the cableplant and is received by the burst receiver. The ratio of the spectrumof the received signal, to the spectrum of the transmitted signal, givesthe estimate of the upstream plant response. Smoothing (such asaveraging over multiple spectra) may be used to reduce the effect ofnoise in this process.

Other means can also be envisioned to compute the upstream plantresponse. A continuous wave (CW) sine wave signal can be swept acrossthe upstream. A chirp signal can be sent. Any form of wideband, or sweptnarrowband, stimulus and response can be used to measure the plantresponse.

This disclosure will concentrate on the example of using an upstreamDOCSIS ranging signal as the stimulus. At each frequency, receivedsamples are captured in the burst receiver during the long rangingburst. The existing DOCSIS ranging bursts contain a long trainingsequence with known QPSK data which is designed to be a good probe ofthe upstream channel, and which has a known, approximately flatfrequency spectrum.

The scheduler should be configured to schedule quiet times (e.g., emptytime division multiple access (TDMA) slots) in the appropriate channelsas the probe signal (sent by probe and received by burst receiver) stepsacross the upstream band. If the probe signal and existing DOCSISchannels are the same bandwidth, at most two channels will requiresimultaneous quiet times. If the probe signal has a wider bandwidth thanexisting DOCSIS channels, more channels may require simultaneous quiettimes.

For each captured segment (which may be of length 4096 samples, as anexample), compute the spectrum, using, for example, an FFT (fast Fouriertransform) or variations of a DFT (discrete Fourier transform) orvariations of an FFT, such as a windowed FFT or a digital filter bank.[See, for example, Crochiere and Rabiner, “Multirate Digital SignalProcessing”, Prentice-Hall, 1983]. The term “FFT” is employed herein inits most general sense to include by reference any form of digitalspectrum generation. More complex signal processing algorithms may beused as well to estimate the spectrum.

It may be advantageous to have the burst receiver capture the digitalsamples and either perform the FFT itself, or hand the samples to anexternal device to perform the FFT processing. In either case, the FFTresults in a sequence of frequency-domain samples. In the example of a4096-point, complex-input FFT, there are 4096 complex output samplesfrom the FFT. In the example of a 4096-point, real-input FFT, there are2048 unique complex output samples from the FFT.

The FFT output samples contain both amplitude and phase information.Both the amplitude and group-delay responses of the upstream cable plantmay be determined. Since both amplitude and phase may be required,averaging of FFT power alone (without phase information) over many FFTsof the same signal band, as is typically done with spectrum analyzers,is in many cases not sufficient. In addition, certain embodiments mayoperate to average the group delay over many FFTs of the same signalband.

The averaging of the amplitude and group delay is done as follows. Foreach FFT taken, the real and imaginary parts (often called “I” and “Q”,respectively) of each frequency domain sample are converted to amplitude(or magnitude) and phase. The amplitude squared (I^ 2+Q^ 2) is ofinterest since it represents the power in each bin, although otherfunctions of the amplitude may also be used. The amplitude squared isaveraged bin-by-bin over many (example 128) FFTs. The averaged FFTs maybe independent, that is, based on disjoint blocks of input samples, orthere may be overlap (such as 50%) between blocks. Windowing orfilter-bank techniques may be applied in the time domain (ahead of theFFT) or in the frequency domain (after the FFT) or by any other standardmeans.

Similarly, the phase information in the output FFT samples is used tocompute the group delay. The group delay is defined as:

-   -   group_delay=−d(phi)/d(omega)

where:

-   -   group_delay is the group delay in seconds    -   phi is the phase in radians    -   omega is the frequency in radians per second.    -   d( )means derivative or differential

The phase is thus processed according to the above equation to give thegroup delay.

The above derivative may be approximated by a simple first-orderdifference. The group delay is then averaged bin-by-bin over many(example 128) FFTs, in the same manner as the magnitude-squared isaveraged. As before, the averaged FFTs may be independent, that is,based on disjoint blocks of input samples, or there may be overlap (suchas 50%) between blocks.

The above FFT processing, including averaging, is done at a given centerfrequency. The center frequency is then incremented and the FFTprocessing is repeated.

Then, such information is spliced or combined together from allfrequency steps to produce a full upstream plant frequency response.

Overlap is used to allow seamless blending of the responses measured atdifferent frequencies. For example, assume that the FFT produces validsamples over a bandwidth equal to ¾ of the symbol rate. In someembodiments, the center frequency may be stepped by ½ the symbol rate,thus allowing for an overlap of ⅛ of the symbol rate at each side of thespectrum. In accordance with such splicing or combination together ortwo successive spectra, care may be taken to adjust blending parameters(for example, gain, offset, and tilt) so that the spectra agree (withminimum mean-squared error, for example) in the overlap region. In thisway the individual narrowband spectra can be spliced together nearlyseamlessly into an overall wideband spectrum.

The above processing was based on the assumption that the transmittedupstream probe signal is approximately flat over the FFT band ofinterest. This should be a good assumption for the DOCSIS rangingtraining signal. However, if the probe signal is not spectrally flat,then it may be determined that either its response is known or can bemeasured and calibrated. Then, the measured FFT is divided by thespectrum of the transmitted training sequence, to get the channelresponse. This calibration can be done using the complex FFT samples(including magnitude and phase) or just using the magnitude of the FFTsamples.

FIG. 11 illustrates an embodiment of a method 1100 for operating atleast one communication device.

Referring to method 1100 of FIG. 11, the method 1100 begins by receivinga ranging burst from at least one additional communication deviceimplemented upstream within a communication system, as shown in a block1110. For example, if the method 1100 is viewed as being performed by acommunication device, then a ranging burst is received after having beentransmitted from at least one additional communication device.

The method 1100 continues by capturing a plurality of sample setscorresponding to the ranging burst respectively in a plurality of centerfrequencies such that each one of the plurality of sample setscorresponding to a respective one of the plurality of centerfrequencies, as shown in a block 1120. That is to say, a number ofrespective sample sets are captured, in each respective sample setcorresponds to a different respective center frequency and/or frequencyband.

The method 1100 then operates by performing spectral analysis of each ofthe plurality of sample sets to generate a plurality of upstream channelresponse estimates such that each one of the plurality of upstreamchannel response estimates corresponding to a respective one of theplurality of sample sets, as shown in a block 1130.

The method 1100 continues by splicing the plurality of upstream channelresponse estimates together to generate a full upstream channel responseestimate, as shown in a block 1140.

FIG. 12 illustrates an alternative embodiment of a method 1200 foroperating at least one communication device.

Referring to method 1200 of FIG. 12, the method 1200 begins by receivinga ranging burst from at least one additional communication deviceimplemented upstream within a communication system, as shown in a block1210. From certain perspectives, the method 1200 of this diagram may beviewed as been performed within the communication device includingequalization capability (e.g., such a communication device may beimplemented as including one or more equalizers).

The method 1200 continues capturing at least one sample setcorresponding to the ranging burst (e.g., corresponding to at least onecenter frequency), as shown in a block 1220. The method 1200 thenoperates by performing equalization processing of the ranging burst (orportion thereof, or signal corresponding thereto or derived therefrom),as shown in a block 1222. The method 1200 continues by capturing atleast one sample set corresponding to the equalized ranging burst (e.g.,corresponding to at least one center frequency), as shown in a block1224. As may be understood, the capturing of the at least one sample asshown within the block 1220 is made with respect to a signal that is notundergone equalization. After the signal has undergone equalization,subsequent capturing of at least one sample set is performed. Then,different respective sample sets are available with respect to at leastone that has not undergone any equalization processing as well as atleast one that has undergone equalization processing.

The method 1200 then operates by performing spectral analysis of each ofthe plurality of sample sets to generate a plurality of upstream channelresponse estimates such that each one of the plurality of upstreamchannel response estimates corresponding to respective one of theplurality of sample sets, as shown in a block 1230. Such spectralanalysis is performed with respect to at least one sample set that hasundergone a position processing in at least one sample set that has notundergone any equalization processing.

The method 1200 continues by splicing the plurality of upstream channelresponse estimates together to generate a full upstream channel responseestimate, as shown in a block 1240.

It is also noted that the various operations and functions as describedwith respect to various methods herein may be performed within any of anumber of types of communication devices, such as using a basebandprocessing module and/or a processing module implemented therein, and/orother components therein. For example, such a baseband processing moduleand/or processing module can generate such signals and perform suchoperations, processes, etc. as described herein as well as performvarious operations and analyses as described herein, or any otheroperations and functions as described herein, etc. or their respectiveequivalents.

In some embodiments, such a baseband processing module and/or aprocessing module (which may be implemented in the same device orseparate devices) can perform such processing, operations, etc. inaccordance with various aspects of the invention, and/or any otheroperations and functions as described herein, etc. or their respectiveequivalents. In some embodiments, such processing is performedcooperatively by a first processing module in a first device, and asecond processing module within a second device. In other embodiments,such processing, operations, etc. are performed wholly by a basebandprocessing module and/or a processing module within one given device. Ineven other embodiments, such processing, operations, etc. are performedusing at least a first processing module and a second processing modulewithin a singular device.

As may be used herein, the terms “substantially” and “approximately”provides an industry-accepted tolerance for its corresponding termand/or relativity between items. Such an industry-accepted toleranceranges from less than one percent to fifty percent and corresponds to,but is not limited to, component values, integrated circuit processvariations, temperature variations, rise and fall times, and/or thermalnoise. Such relativity between items ranges from a difference of a fewpercent to magnitude differences. As may also be used herein, theterm(s) “operably coupled to”, “coupled to”, and/or “coupling” includesdirect coupling between items and/or indirect coupling between items viaan intervening item (e.g., an item includes, but is not limited to, acomponent, an element, a circuit, and/or a module) where, for indirectcoupling, the intervening item does not modify the information of asignal but may adjust its current level, voltage level, and/or powerlevel. As may further be used herein, inferred coupling (i.e., where oneelement is coupled to another element by inference) includes direct andindirect coupling between two items in the same manner as “coupled to”.As may even further be used herein, the term “operable to” or “operablycoupled to” indicates that an item includes one or more of powerconnections, input(s), output(s), etc., to perform, when activated, oneor more its corresponding functions and may further include inferredcoupling to one or more other items. As may still further be usedherein, the term “associated with”, includes direct and/or indirectcoupling of separate items and/or one item being embedded within anotheritem. As may be used herein, the term “compares favorably”, indicatesthat a comparison between two or more items, signals, etc., provides adesired relationship. For example, when the desired relationship is thatsignal 1 has a greater magnitude than signal 2, a favorable comparisonmay be achieved when the magnitude of signal 1 is greater than that ofsignal 2 (or alternatively, when the magnitude of signal 2 is less thanthat of signal 1).

As may also be used herein, the terms “processing module”, “module”,“processing circuit”, and/or “processing unit” (e.g., including variousmodules and/or circuitries such as may be operative, implemented, and/orfor encoding, for decoding, for baseband processing, etc.) may be asingle processing device or a plurality of processing devices. Such aprocessing device may be a microprocessor, micro-controller, digitalsignal processor, microcomputer, central processing unit, fieldprogrammable gate array, programmable logic device, state machine, logiccircuitry, analog circuitry, digital circuitry, and/or any device thatmanipulates signals (analog and/or digital) based on hard coding of thecircuitry and/or operational instructions. The processing module,module, processing circuit, and/or processing unit may have anassociated memory and/or an integrated memory element, which may be asingle memory device, a plurality of memory devices, and/or embeddedcircuitry of the processing module, module, processing circuit, and/orprocessing unit. Such a memory device may be a read-only memory (ROM),random access memory (RAM), volatile memory, non-volatile memory, staticmemory, dynamic memory, flash memory, cache memory, and/or any devicethat stores digital information. Note that if the processing module,module, processing circuit, and/or processing unit includes more thanone processing device, the processing devices may be centrally located(e.g., directly coupled together via a wired and/or wireless busstructure) or may be distributedly located (e.g., cloud computing viaindirect coupling via a local area network and/or a wide area network).Further note that if the processing module, module, processing circuit,and/or processing unit implements one or more of its functions via astate machine, analog circuitry, digital circuitry, and/or logiccircuitry, the memory and/or memory element storing the correspondingoperational instructions may be embedded within, or external to, thecircuitry comprising the state machine, analog circuitry, digitalcircuitry, and/or logic circuitry. Still further note that, the memoryelement may store, and the processing module, module, processingcircuit, and/or processing unit executes, hard coded and/or operationalinstructions corresponding to at least some of the steps and/orfunctions illustrated in one or more of the Figures. Such a memorydevice or memory element can be included in an article of manufacture.

The present invention has been described above with the aid of methodsteps illustrating the performance of specified functions andrelationships thereof. The boundaries and sequence of these functionalbuilding blocks and method steps have been arbitrarily defined hereinfor convenience of description. Alternate boundaries and sequences canbe defined so long as the specified functions and relationships areappropriately performed. Any such alternate boundaries or sequences arethus within the scope and spirit of the claimed invention. Further, theboundaries of these functional building blocks have been arbitrarilydefined for convenience of description. Alternate boundaries could bedefined as long as the certain significant functions are appropriatelyperformed. Similarly, flow diagram blocks may also have been arbitrarilydefined herein to illustrate certain significant functionality. To theextent used, the flow diagram block boundaries and sequence could havebeen defined otherwise and still perform the certain significantfunctionality. Such alternate definitions of both functional buildingblocks and flow diagram blocks and sequences are thus within the scopeand spirit of the claimed invention. One of average skill in the artwill also recognize that the functional building blocks, and otherillustrative blocks, modules and components herein, can be implementedas illustrated or by discrete components, application specificintegrated circuits, processors executing appropriate software and thelike or any combination thereof.

The present invention may have also been described, at least in part, interms of one or more embodiments. An embodiment of the present inventionis used herein to illustrate the present invention, an aspect thereof, afeature thereof, a concept thereof, and/or an example thereof. Aphysical embodiment of an apparatus, an article of manufacture, amachine, and/or of a process that embodies the present invention mayinclude one or more of the aspects, features, concepts, examples, etc.described with reference to one or more of the embodiments discussedherein. Further, from figure to figure, the embodiments may incorporatethe same or similarly named functions, steps, modules, etc. that may usethe same or different reference numbers and, as such, the functions,steps, modules, etc. may be the same or similar functions, steps,modules, etc. or different ones.

Unless specifically stated to the contrary, signals to, from, and/orbetween elements in a figure of any of the figures presented herein maybe analog or digital, continuous time or discrete time, electrical,optical, and single-ended or differential. For instance, if a signalpath is shown as a single-ended path, it also represents a differentialsignal path. Similarly, if a signal path is shown as a differentialpath, it also represents a single-ended signal path. While one or moreparticular architectures are described herein, other architectures canlikewise be implemented that use one or more data buses not expresslyshown, direct connectivity between elements, and/or indirect couplingbetween other elements as recognized by one of average skill in the art.

The term “module” is used in the description of the various embodimentsof the present invention. A module includes a functional block that isimplemented via hardware to perform one or module functions such as theprocessing of one or more input signals to produce one or more outputsignals. The hardware that implements the module may itself operate inconjunction software, and/or firmware. As used herein, a module maycontain one or more sub-modules that themselves are modules.

While particular combinations of various functions and features of thepresent invention have been expressly described herein, othercombinations of these features and functions are likewise possible. Thepresent invention is not limited by the particular examples disclosedherein and expressly incorporates these other combinations.

What is claimed is:
 1. An apparatus comprising: a communicationinterface; and a processor configured to: receive, via the communicationinterface, a ranging burst transmitted via a channel from anotherapparatus; capture a plurality of sample sets corresponding to theranging burst, wherein each sample set of the plurality of sample setscorresponds to a respective center frequency of a plurality of centerfrequencies of a plurality of sub-channels distributed across thechannel; perform fast Fourier transform (FFT) processing of each sampleset of the plurality of sample sets to generate a plurality of channelresponse estimates, wherein each channel response estimate of theplurality of channel response estimates corresponds to a respectivechannel response estimate of a respective sub-channel of the pluralityof sub-channels; and splice the plurality of channel response estimatestogether to generate a full channel response estimate of the channel. 2.The apparatus of claim 1, wherein the processor further comprising: anequalizer configured to process the ranging burst, wherein: at least oneof the plurality of sample sets corresponds to the ranging burstcaptured before undergoing processing by the equalizer; and at least oneof the plurality of sample sets corresponds to the ranging burstcaptured after undergoing processing by the equalizer.
 3. The apparatusof claim 1, wherein: at least one of the plurality of sample setscorresponding to a plurality of gain offsets corresponds to the rangingburst; and at least one of the plurality of sample sets corresponding toa plurality of timing offsets corresponds to the ranging burst.
 4. Theapparatus of claim 1, wherein the ranging burst includes a long trainingsequence having quadrature phase shift keying (QPSK) modulated data. 5.The apparatus of claim 1 further comprising: a communication device thatis operative within at least one of a satellite communication system, awireless communication system, a wired communication system, afiber-optic communication system, a mobile communication system, or acable system.
 6. An apparatus comprising: a communication interface; anda processor configured to: capture a plurality of sample setscorresponding to a ranging burst that is received via the communicationinterface, wherein each sample set of the plurality of sample setscorresponds to a respective center frequency of a plurality of centerfrequencies of a plurality of sub-channels distributed across a channel;perform spectral analysis of each sample set of the plurality of samplesets to generate a plurality of channel response estimates, wherein eachchannel response estimate of the plurality of channel response estimatescorresponds to a respective channel response estimate of a respectivesub-channel of the plurality of sub-channels; and splice the pluralityof channel response estimates together to generate a full channelresponse estimate of the channel.
 7. The apparatus of claim 6, whereinthe processor further comprising: an equalizer to process the rangingburst, wherein: at least one of the plurality of sample sets correspondsto the ranging burst captured before undergoing processing by theequalizer; and at least one of the plurality of sample sets correspondsto the ranging burst captured after undergoing processing by theequalizer.
 8. The apparatus of claim 6, wherein at least one of theplurality of sample sets corresponding to a plurality of gain offsetscorresponds to the ranging burst.
 9. The apparatus of claim 6, whereinat least one of the plurality of sample sets corresponding to aplurality of timing offsets corresponds to the ranging burst.
 10. Theapparatus of claim 6, wherein the ranging burst includes a long trainingsequence having quadrature phase shift keying (QPSK) modulated data. 11.The apparatus of claim 6, wherein the processor is further configuredto: perform fast Fourier transform (FFT) processing of each sample setof the plurality of sample sets to generate the plurality of channelresponse estimates.
 12. The apparatus of claim 6, wherein the pluralityof center frequencies are uniformly spaced apart in frequency across thechannel, wherein a first of the plurality of center frequencies isseparated from a second of the plurality of center frequencies by afrequency increment and the second of the plurality of centerfrequencies is separated from a third of the plurality of centerfrequencies by the frequency increment.
 13. The apparatus of claim 6further comprising: a communication device that is operative within atleast one of a satellite communication system, a wireless communicationsystem, a wired communication system, a fiber-optic communicationsystem, a mobile communication system, or a cable system.
 14. A methodfor execution by a communication device, the method comprising: via aninput of the communication device, receiving a ranging burst fromanother communication device; capturing a plurality of sample setscorresponding to the ranging burst, wherein each sample set of theplurality of sample sets corresponds to a respective center frequency ofa plurality of center frequencies of a plurality of sub-channelsdistributed across a channel; performing spectral analysis of eachsample set of the plurality of sample sets to generate a plurality ofchannel response estimates, wherein each channel response estimate ofthe plurality of upstream channel response estimates corresponds to arespective channel response estimate of a respective sub-channel of theplurality of sub-channels; and splicing the plurality of channelresponse estimates together to generate a full channel response estimateof the channel.
 15. The method of claim 14 further comprising: operatingan equalizer of the communication device to process the ranging burst;capturing at least one of the plurality of sample sets corresponding tothe ranging burst before the ranging burst undergoing processing by theequalizer; and capturing at least one of the plurality of sample setscorresponding to the ranging burst after the ranging burst undergoingprocessing by the equalizer.
 16. The method of claim 14, wherein: atleast one of the plurality of sample sets corresponds to a plurality ofgain offsets corresponding to the ranging burst; and at least one of theplurality of sample sets corresponds to a plurality of timing offsetscorresponding to the ranging burst.
 17. The method of claim 14, whereinthe ranging burst includes a long training sequence having quadraturephase shift keying (QPSK) modulated data.
 18. The method of claim 14further comprising: performing fast Fourier transform (FFT) processingof each sample set of the plurality of sample sets to generate theplurality of channel response estimates.
 19. The method of claim 14,wherein the plurality of center frequencies are uniformly spaced apartin frequency across the channel, wherein a first of the plurality ofcenter frequencies is separated from a second of the plurality of centerfrequencies by a frequency increment and the second of the plurality ofcenter frequencies is separated from a third of the plurality of centerfrequencies by the frequency increment.
 20. The method of claim 14,wherein: the communication device is operative within at least one of asatellite communication system, a wireless communication system, a wiredcommunication system, a fiber-optic communication system, a mobilecommunication system, or a cable system.